PROJECT SUMMARY/ABSTRACT Complex health interventions (CHIs), including clinical, health service delivery and public health interventions with multiple adaptable components addressing multiple intervention targets are increasingly prevalent within the U.S. health system. CHIs represent promising solutions to complex health problems requiring simultaneous, coordinated efforts targeting root causes at the patient, clinician, health system, community, and/or regional, state and national levels. CHIs pose unique challenges and barriers to research and evaluation, however: prevailing health-related research approaches are optimized for simple, fixed, homogeneous interventions (e.g., pharmaceutical interventions) delivered with high levels of standardization and fidelity, but are poorly equipped to handle complex, multiple-component, heterogeneous and adaptable interventions. Furthermore, the primary goals of research on simple interventions ? e average effect size estimates and answers to questions such as ?is intervention A effective?? or ?is intervention A superior to intervention B?? ? are not useful for CHIs, for which the prevailing answer is generally ?it depends.? Decision makers require guidance to support multiple decisions for CHIs, including (a) selecting interventions matched to features of their settings, (b) adapting CHIs to meet local circumstances, and (c) managing local conditions to enhance intervention effectiveness through improved intervention-context concordance. Research approaches capable of guiding the complex, multiple decisions and management actions required for CHIs are very different from those optimized to produce estimates of average intervention effect sizes. CHIs require distinctive study designs, intervention delivery and adaptation activities, data collection and analysis methods, and other study features. The expert meeting proposed in this application will convene key policy, practice and research leaders to (1) review the goals and desired outcomes of research evaluating CHIs and available methods standards and guidance for such studies, (2) assess prevailing research practices for CHIs and the relationship between prevailing vs. recommended practices, (3) identify barriers and facilitators to improved research practices, and (4) produce guidance and a set of recommendations for policy, practice and research stakeholder activities that will strengthen research on CHIs. The proposed conference will include pre-meeting preparation, a structured three-day meeting containing panel sessions and intensive small-group working sessions, and post-meeting work to operationalize the recommendations and facilitate their implementation. The initiative will facilitate improvement in the quality and value of research on complex interventions to enhance the contributions of this research to (a) improved evidence, insights and understanding of the operation and effects of CHIs and to (b) improvements in clinicians' and healthcare leaders' success in appropriately selecting, implementing and managing CHIs.